1. Field of the Invention
The present invention relates to a catheter insertion device capable of securing a passage communicating with a blood vessel in such a manner that a device comprising an outer catheter and an inner needle received thereby is thrust into a blood vessel, and when the outer catheter has entered into the blood vessel, the inner needle is pulled out to secure a passage communicating with a blood vessel by means of the outer catheter.
2. Description of the Prior Art
The catheter insertion device has been widely used for securing a lumen for introducing a catheter by thrusting the catheter insertion device into a blood vessel located in a relatively deep part of the body tissue of a patient. A conventional catheter insertion device with a typical arrangement will be described hereinunder, with reference to the accompanying drawings for easier understanding.
The catheter insertion device, shown in FIG. 1, comprising an inner needle 1 and an outer catheter 2 fitted on the outside of the inner needle 1, inevitably makes an incision 4 with a size (a) equal to the beveled surface width of the inner needle 1, i.e., the diameter of the inner needle 1 when the catheter insertion device is thrust into a blood vessel 3 as shown in FIG. 2. Therefore, hemostasis after the needle is pulled out becomes more difficult with the increase in the outside diameter of the inner needle 1. On the other hand, when the catheter insertion device is used as a needle for introducing an angiography catheter, the inner catheter is pulled out with a guide wire being indwelled in the blood vessel. In other words, after the catheter insertion device is thrust into the blood vessel, the inner needle is pulled out with the outer catheter left and subsequently the guide wire is introduced into the blood vessel by using the outer catheter as an introducing needle. Under this condition, a large amount of blood flows out from the incision to the outside until an angiography catheter, not shown, is introduced into the blood vessel with the guide wire used as a guide, because the guide wire used has an outside diameter equal to or smaller than the width (a) of the incision 4.
The above-mentioned problems have been solved by means of a catheter insertion device shown in FIG. 3. The catheter insertion device is provided with a dilator 5 disposed between the inner needle 1 and the outer catheter 2 and having on its end outer surface a dilator tapered tip portion 5a capable of enlarging the incision 4 in the blood vessel formed by means of the beveled point of the inner needle 1. Accordingly, although the width (a) of the incision 4 in the blood vessel 3 shown in FIG. 2 is equal to the diameter of the inner needle 1 even if the catheter insertion device of this type is used, the incision becomes smaller and hemostasis becomes easier because the diameter of the inner needle 1 is smaller than the inside diameter of the outer catheter 2 (e.g., the inside diameter of the outer catheter 2 is 1 mm while the outside diameter of the inner needle 1 is 0.8 mm). Moreover, when the catheter insertion device is used as a needle for introducing the angiography catheter, the guide wire is clamped by the blood vessel wall when the guide wire is being indwelled in the blood vessel, because the guide wire diameter (e.g., 1 mm .phi.) is larger than the blood vessel incision (e.g., 0.8 mm) shown in FIG. 2. Therefore, only a small amount of blood leaks from the incision 4 (however, the relationship between the ratio of the blood vessel incision to the guide wire diameter and the amount of leakage blood has not been accurately known).
However, the production cost of the catheter insertion device of this kind is considerably higher than that of the catheter insertion device shown in FIG. 1 because the former has the dilator 5. Moreover, because the penetration resistance of the tip of the dilator tapered tip portion 5a is added to the penetration resistance of the catheter insertion device shown in FIG. 1, the patient suffers a correspondingly larger pain. Furthermore, because there is the dilator 5 and consequently the length l.sub.1 between the beveled point of the inner needle 1 and the outer catheter tapered portion is larger than that of the catheter insertion device shown in FIG. 1, it is frequent that the end of the outer catheter 2 does not enter into the blood vessel even when it is confirmed that the beveled portion 1a of the inner needle 1 is present in the blood vessel by means of flushback after the catheter insertion device is thrust into the blood vessel, resulting in low reliability in securing a passage communicating with a blood vessel. FIG. 4 is a graph showing the change in the penetration resistance of the catheter insertion device. A peak b is obtained at a point of time the incision is formed in the blood vessel by the beveled point of the inner needle, a peak c is obtained at a moment the dilator enters into the incision, and a peak d is obtained at a moment the outer catheter enters into the incision. The patient feels pain at peaks and particularly suffers a large pain at each of the peaks b, c and d. When the diameter of the inner needle is not more than 40% of the outside diameter of the outer catheter, the enlargement of the incision in the blood vessel becomes great, so that a large pain is inflicted on the patient.